The present invention relates to a circuit breaker such as an autobreaker that is applied to the protection of a low-voltage distributing facility from overcurrents, the circuit breaker being provided with an auxiliary switch that acts as an attached device that enables the breaker to detect the ON and OFF status of main circuit contacts as electrical signals.
FIGS. 4(a) and 4(b) show the construction of a circuit breaker such as an autobreaker having an internal attached switch installed in the main body thereof. In these figures, reference numeral 1 denotes a main body case of the breaker, 2 denotes a main-circuit breaking section incorporated in the case 1, 3 denotes a toggle-link opening and closing mechanism section, 4 denotes an overload current tripping device, 5 denotes an operating handle, 6 denotes an opening and closing lever, described later in detail, 7 denotes a cassette-type attached switch (auxiliary switch for detecting the ON and OFF status of main circuit contacts as electric signals) installed in the main body case 1 as an internal attached device (option), and 8 denotes another attached switch (alarm switch responsive to an output from an alarm output plate that detects the trip operation of the breaker).
The opening and closing mechanism section 3 comprises a toggle link mechanism responsive to an ON/OFF operation of the operating handle 5 or an output from the overload current tripping device 4, and the opening and closing lever 6 that operates synchronously with the toggle link mechanism to open or close the main circuit contacts. Furthermore, the opening and closing lever 6 is a seesaw-type lever that pivots vertically around a support shaft 6b as shown in FIG. 5. The opening and closing lever 6 has an operating end 6a located opposite. the top of a contact shoe holder 2b supporting a movable contact shoe 2a of the main circuit contact breaking section 2 as shown in FIG. 7. During an OFF operation, the opening and closing lever 6 is driven clockwise by the force of an urge spring to strike the movable contact shoe holder to open the main circuit contacts. In contrast, during an ON operation, the opening and closing lever 6 is pivoted counterclockwise, causing the movable contact shoe holder 2b to recede upward, so that following this motion the main circuit contacts are closed. Furthermore, a tip 6c (see FIG. 5) of the other end of the opening and closing lever 6 functions as an opening and closing actuator for attached switch 7, installed in the main body case 1.
In the above construction, when the operating handle 5 is manually set to the ON/OFF position, the opening and closing lever 6 of the opening and closing mechanism section 3 is pivoted to open or close the main circuit contacts of the breaking section 2. Conversely, if an overload current flows through the main circuit, an output signal from the tripping device 4 causes the opening and closing mechanism section 3 to perform a trip operation to open the main circuit contacts, a commonly-known process.
Unlike the above-described process, the attached switch 7 has a fixed contact 7b, a bridging movable contact 7c, a movable contact shoe holder (vertically movable slider) 7d, and a return spring 7e for urging and biasing the movable contact 7c to an opened and separated position, all these components being incorporated in the case 7a. Furthermore, the arm-shaped operating lever 7f is connected to the movable contact shoe holder 7d and exposed from a front surface of the case 7a, as shown in FIGS. 6(a) through 6(c); the attached switch 7 is a spring return limit switch. The attached switch 7 is installed in an accessory housing section defined in a top surface side of the main body case 1 like a cassette, as shown in FIG. 3. At this installed position, the operating lever 7f is located opposite the tip 6c of the opening and closing lever 6 of the breaker main body, as illustrated in FIG. 5.
The attached switch 7 operates as follows. In an ON state in which the main circuit contacts of the breaker are closed, the tip of the opening and closing lever 6, which has been pivoted counterclockwise, is lowered to push down the movable contact shoe holder 7d of the attached switch 7 using the force of the return spring 7e, thereby opening and separating the movable contact shoe 7c from the fixed contact shoe 7b (the switch contacts are turned off), as illustrated in FIG. 7. Then an OFF signal from this switch allows the detection of the ON state of the main circuit contacts of the breaker. Conversely, in an OFF state in which the trip operation is performed due to a handle operation or the tripping device to open the main circuit contacts, the tip 6c of the opening and closing lever 6, which has been pivoted clockwise, thrusts the operating lever 7f of the attached switch 7 upward against the force of the return spring 7e to close the movable contact 7c/fixed contact 7b, thereby causing a main circuit contact OFF signal to be output to an exterior. The attached switch 7 in the illustrated example performs ON and OFF operations in response to the opening and closing of the main circuit contacts of the breaker, respectively. In contrast, however, an attached switch that performs the ON operation when the main circuit contacts are closed, and the OFF operation when the contacts are opened, may be used.
With the above construction, in which the attached switch 7 is composed of a spring-return switch and in which the operating lever 7f is located opposite the tip 6c of the opening and closing lever 6 of the breaker main body, if an error occurs in which the built-in contacts of the attached switch are welded together, then a misdetection problem may result as follows:
If the attached switch 7 operates correctly, the attached switch 7 responds to the pivoting operation of the opening and closing lever 6 of the breaker main body to correctly detect the ON/OFF state of the circuit breaker, as described in FIG. 7. If, however, the built-in contacts of the attached switch 7 are welded together, when the main circuit contacts are turned on again after the trip operation of the circuit breaker, the attached switch 7 remains contact-welded and does not perform the OFF operation, even though the opening and closing lever 6 is pivoted counterclockwise to leave the operating lever 7f of the attached switch 7 to recede downward. In this regard, the force of the return spring 7e shown in FIG. 6(c) is not great enough to cause the welded contacts to be separated from each other. Thus, although the circuit breaker is actually in the ON state, the attached switch 7 continues to output a signal indicating that the main circuit contacts of the breaker are in the OFF state. Consequently, a maintenance worker may mistakenly determine that the circuit breaker is off, and if the worker touches a load-side circuit, he or she may unexpectedly get an electric shock.
The present invention is provided in view of these points, and it is an object thereof to provide an improved circuit breaker in which, even if the built-in contacts of the attached switch installed in the circuit breaker are welded together during operation, the contacts of the welded attached switch are forcibly separated from each other using the force of the pivoting operation of the opening and closing lever of the breaker main body so that the ON/OFF states of the main circuit contacts can be correctly detected.
To attain the above object, the present invention provides a circuit breaker comprising an opening and closing mechanism section for opening and closing the main circuit contacts according to a handle operation or an output from an overload current tripping device, the opening and closing mechanism section including a seesaw-type opening and closing lever that pivots vertically, the circuit breaker furthermore comprising a cassette-type attached switch installed in an accessory housing section formed in the main body case of the breaker so as to follow the movement of the opening and closing lever to detect the ON or OFF status of the main circuit contacts as an electrical signal, the attached switch having an operating lever moving vertically and placed opposite a tip of the opening and closing lever when the attached switch is installed in the accessory housing section of the main body case, wherein an interlocking hook is attached to the operating lever, which is then engaged in a position where the attached switch is installed with the opening and closing lever of the breaker main body so as to hook a tip thereof, so that motion of the opening and closing lever away from the operating lever of the attached switch is transmitted to the operating lever via the interlocking hook, thereby forcibly operating the attached switch in this direction (a first aspect of the invention).
Furthermore, when the attached switch having the above configuration is installed in an accessory housing section, in order to locate the interlocking hook of the attached switch in a position where the interlocking hook engages with the opening and closing lever, the interlocking hook is shaped like a ring, and an attached switch housing box section formed in the main body case of the breaker has a hook guide at a bottom thereof for guiding, in a position where the attached switch is installed, the interlocking hook to a position where the interlocking hook is engaged with the opening and closing lever.
With the above configuration, if an error occurs in which the built-in contacts of the attached switch are welded together during operation and cannot be opened by themselves, then the force of a pivoting operation of the opening and closing lever associated with a turn-on operation of the circuit breaker is used to forcibly separate the contacts of the attached switch in order to recover from the contact welding. Consequently, the attached switch is prevented from outputting misdetection signals, thereby increasing the reliability of the breaker.